A surface wave component comprises at least one electro-acoustic transducer that is arranged on a crystalline or ceramic piezoelectric thin film. The electro-acoustic transducer possesses a periodic finger structure, whereby the fingers are as a rule alternately connected to two different collector electrodes (busbars). The period of the finger structure determines the resonance frequency of the transducer, which corresponds to the frequency in which the electro-acoustic conversion ensues with the greatest degree of efficiency. Given a surface wave resonator, the impedance of the resonator is approximately zero at the resonance frequency.
The important properties of the transducer are substantially determined by number, width, separation and connection sequence of the electrode fingers, as well as by the aperture of the transducer. These are, as a rule, selected such that, as exclusively as possible, only an acoustic vibration mode is excited, on which the design is optimized with regard to the cited variable parameters.
An application for surface wave components is the assembly of reactance filters made from surface wave single-port resonators. An important characteristic of this reactance filter is the insertion dampening, which corresponds to the maximum dampening of a signal passing through the filter in the transmission range. Everything that the insertion dampening increases degrades the performance of the overall system, such that here as well the least losses are to be prevented.
Resonators that are used in the parallel branch of reactance filters should exhibit above their resonance frequency an optimally vanishing real portion of the input admittance. A real portion (differing there from zero) of the input admittance of the parallel resonator namely leads to an unwanted conductivity in the transmission range, to a drain of the signal energy, and to an increased insertion dampening. The input admittance of a single-port resonator typically used today now shows precisely a shoulder in this range, that therewith leads to an increased input dampening in a reactance filter. However, for this or also even for other known shoulders, as of yet no measures are known in order to effectively suppress them.